The invention generally relates to radiographic imaging and, more particularly, relates to a method and apparatus for reading a computed radiography phosphor medium that has been exposed by x-rays by supplying pumping light thereto.
It is well known that by using x-ray systems, items can be visualized within the human body or within industrial products, or the like. Current x-ray systems often use x-ray film, which must be developed or use computed tomography installations which are very expensive and require large amounts of computer power.
In addition, systems exist which use a technique called computer radiography, in which a sample or a patient is exposed with x-rays and a latent x-ray image is formed on a phosphor-containing sheet similar to a sheet of film. The phosphor-containing sheet may typically include a rare earth, such as europium, in combination with barium and fluorine. Other sheet formulations also are available. The sheet, which must be kept in the dark, is then imaged by exposing the sheet to a raster-scanned laser beam causing areas which have preferentially received x-ray energy to phosphoresce yielding an image.
While the system is convenient and allows the reuse of the sheets multiple numbers of time, it does suffer from certain drawbacks. It is difficult to obtain high-spatial resolution because the pumping laser beam, although only covering a small spot-size at a time, tends to leave illumination energy behind, which causes bloom; thereby smearing the image and reducing its resolution. This is because the image is built up in the way that an image might be with a flying spot device wherein only a single optical detector is used. The single optical detector can capture radiation from almost any direction. Thus, the single detector is unable to determine whether the photons it is receiving are coming from unwanted bloom or coming from active phosphorescence.
In addition, the existing systems which typically use a laser, either operate the laser at about 630 to 650 nanometers or, in the near infrared range, at about 930 nanometers. A single laser cannot be used for both wavelengths. Because there are differing types of latent imaging materials used for computer tomography, not all phosphoresce either with red pumping or with infrared pumping. Thus, a scanner which uses a pumping laser in the red or infrared region, cannot accept latent images formed for pumping in the opposite region.
Furthermore, the raster-scanned laser system introduces spatial nonlinearities in the image which must be compensated for. The non-linearities are due to the difference in the effective scan rate when the beam is substantially perpendicular to the latent image film at the center portion of the film and when it is sweeping at a relatively large angle with respect to the medium near its edges. As a result, since the only way to costruct the image coming back is based on pumping beam timing and orientation, elaborate methods must be taken in order to relinearize the beam scan in order to construct an undistorted image.
What is needed then, is a system and apparatus which can quickly and conveniently provide highly-accurate computed radiography images without the need for expensive equipment.
The present invention is embodied in an apparatus and method for radiographic imaging wherein a substrate is exposed to x-radiation to form a latent image thereon. The apparatus comprises a plurality of light emitting diodes emitting incoherent light at two different visible wavelengths and one infrared wavelength. The LEDs supply light to a plurality of optical pumping fibers which deliver the incoherent light to the radiographic medium. The optical pumping fibers have their delivery ends aligned in a linear array and a motor causes the plate or radiographic medium to be moved under the linear fiber array as it is exposed to the pumping light from the fibers. In addition the fibers are multiplexed in groups of 64 so that there is no unwanted bloom from one excitation or pumping fiber to the next at any one time. This improves the optical resolution provided by the pumping light.
A second plurality of optical fibers each having a diameter of about 500 microns collect the emitted light and deliver the emitted light to photodiodes or other optical transducers which change the light intensity to an electrical signal. That signal is supplied to a processor which generates an image signal. The image signal may then be used to generate an image representative of the latent x-ray image on the radiographic substrate.
It is a principal object of the present invention to provide a high resolution radiographic imaging apparatus.
It is another object of the present invention to provide a high resolution radiographic image using incoherent low cost optical sources such as light emitting diodes as pump sources.
Other aspects and advantages of the present invention will become obvious to one of ordinary skill in the art upon a perusal of the following specification and claims in light of the accompanying drawings.